91 honda accord automatic transmission. Would love some advice on ideas for what to replace first. This started with driving along at 50 mph when my car suddenly downshifted. I wasn't able to pull over so I limped doing 30 to a friends house 2 miles away. If I went over 30 it would shift up then back down just randomly a mess with shifting. I parked it. Decided it needed to be farther off road so I backed it up, when I tried to go forward it just revved, wouldn't move, in any gear. I put it in park and then it locked in park. Had to take the console off and use the switch to get it out of park. Was able to drive it the next 2 miles home to my house today, same as before, going about 30 before it started shifting back and forth severely. My sort of mechanically inclined friend said to change my Neutral Safety Switch but I'm not sure if that is really fitting with all the symptoms. Any advice please? Thank you

 

it's possible for the neutral safety switch to go bad and that would prevent you from getting out of park, given the timing of the issues happening at the same time you can try swapping it out for another

probably grab another from the junkyard

 

A shift interlock will not cause a vehicle to shift on its own "Accord" lol..... (Anyways) I'm going to assume that "downshifting" to you is going to a lower gear number, and "upshifting" is going to a higher gear number for clarity. If this is wrong to you, you need to tell us. At 50mph you should be in 4th gear with the TCC locked up.

So, 4th gear + TCC at 50 mph. TCC unlocks and downshifts to an unknown gear (3 is likely, 2 is possible). Going faster forces a 3 to 4 shift (or 2 to 3), then back to 3rd (or 4th). You park and lock the car after backing it up and are unable to drive forward. The next day you override the shift interlock, and drive it under the same conditions to your house.

Assuming I have this right, the shift interlock is either a second problem, or a symptom of a low voltage battery. Before I can reliably tell you anything more, you need to tell us the following:

What is the level of transmission fluid.
When did this problem first start.
What maintenance or repairs were done prior to the issue starting.
Are you leaking anything,

I have a lot of speculation but I am not willing to divulge it and lead you on a goose-chase without as much precise information as you can possibly provide. I can't see your car after all.

 

Thank you both for the replies. Information you requested:
Transmission fluid level is good, fluid was replaced 2 weeks ago with the honda recommended brand, forget the name, sorry. Besides oil changes and various fluid filling that is only maintenance or repairs done since I changed my main relay about 6 months ago for a no starting issue.
Problem started yesterday.
Leaking only slight amount of oil, I've been told is in normal range for an old car with 250k miles on it, doesn't leak enough to have to put any in between regular oil changes.

Driving it home today it never went past 3rd into 4th, it was shifting from 2nd to 3rd and back to 2nd too severely for me to try to push it past 3rd. Even when it should have been staying in 3rd it would shift down to 2nd at any time. It seemed that the more over 30 I went the worse it got but I wouldn't say that 100%, might just be my own perception.

 

I didn't read it as shifting on its own, I read it as just coming out of gear.

 

Bad shift control solenoid was the problem. All fixed and shifting great now.